Here, let me put this in easier terms: everyone is thinking of an American (or maybe even a UK) work week where it's 40 hours, 5 days a week, 8 hours a day.

Japan is not like this. Just a normal salaryman can work 49+ hours a week, and while they have time off they CAN use (not including the one day holidays they have across the country) most don't. The reason? It's seen as disrespectful. So while they may have MAYBE 19 days or so of vacation time they can take, they don't. They don't want to kick back while their peers and coworkers are working and picking up their slack and going from a 12-14 hour day to a 16-17 hour day at work while that person is on a two day paid vacation.

That's why the devs taking a break after working ridiculous hours to pound out a core game, 5 patches, and a huge xpac at the same time as developing your content patches, is such a big deal. If my day consisted of reading lines of code to make sure things weren't buggy, and if I did that for upwards of 15 hours a day? I'd want a break too, even if it were for 4 days. Japan has a high suicide rate due to schooling/work conditions, and this is precisely why (out of 100k people, 19.4 people will take their own lives, for clarification.) They also have a fairly high amount of stress-related illness/deaths that come from overworking themselves.

So, there's your reasoning on why the devs needed a week, likely a week that they were reluctant to take, before jumping into making a content patch: because they're likely to work themselves to death if they don't.

tl;dr, their culture is radically different from everyone else's.